fix: resolve PHPStan static analysis warnings

app/Models/Order.php

@@ -3,7 +3,38 @@
 namespace App\Models;
 
 use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Relations\BelongsTo;
+use Illuminate\Database\Eloquent\Relations\HasMany;
 
+/**
+ * App\Models\Order
+ *
+ * @property int $id
+ * @property int $user_id
+ * @property int $plan_id
+ * @property int|null $payment_id
+ * @property int $period
+ * @property string $trade_no
+ * @property int $total_amount
+ * @property int|null $handling_amount
+ * @property int|null $balance_amount
+ * @property int $type
+ * @property int $status
+ * @property array|null $surplus_order_ids
+ * @property int|null $coupon_id
+ * @property int $created_at
+ * @property int $updated_at
+ * @property int|null $commission_status
+ * @property int|null $invite_user_id
+ * @property int|null $actual_commission_balance
+ * @property int|null $commission_rate
+ * @property int|null $commission_auto_check
+ * 
+ * @property-read Plan $plan
+ * @property-read Payment|null $payment
+ * @property-read User $user
+ * @property-read \Illuminate\Database\Eloquent\Collection<int, CommissionLog> $commission_log
+ */
 class Order extends Model
 {
     protected $table = 'v2_order';
@@ -12,7 +43,8 @@ class Order extends Model
     protected $casts = [
         'created_at' => 'timestamp',
         'updated_at' => 'timestamp',
-        'surplus_order_ids' => 'array'
+        'surplus_order_ids' => 'array',
+        'handling_amount' => 'integer'
     ];
 
     const STATUS_PENDING = 0; // 待支付
@@ -40,21 +72,34 @@ class Order extends Model
         self::TYPE_RESET_TRAFFIC => '流量重置',
     ];
 
-    public function payment()
+    /**
+     * 获取与订单关联的支付方式
+     */
+    public function payment(): BelongsTo
     {
         return $this->belongsTo(Payment::class, 'payment_id', 'id');
     }
 
-    public function user()
+    /**
+     * 获取与订单关联的用户
+     */
+    public function user(): BelongsTo
     {
         return $this->belongsTo(User::class, 'user_id', 'id');
     }
-    public function plan()
+
+    /**
+     * 获取与订单关联的套餐
+     */
+    public function plan(): BelongsTo
     {
-        return $this->belongsTo(Plan::class);
+        return $this->belongsTo(Plan::class, 'plan_id', 'id');
     }
 
-    public function commission_log()
+    /**
+     * 获取与订单关联的佣金记录
+     */
+    public function commission_log(): HasMany
     {
         return $this->hasMany(CommissionLog::class, 'trade_no', 'trade_no');
     }